PMID- 33914656
OWN - NLM
STAT- MEDLINE
DCOM- 20210630
LR  - 20210812
IS  - 1522-1601 (Electronic)
IS  - 0161-7567 (Linking)
VI  - 130
IP  - 6
DP  - 2021 Jun 1
TI  - Motor unit firing rates during constant isometric contraction: establishing and 
      comparing an age-related pattern among muscles.
PG  - 1903-1914
LID - 10.1152/japplphysiol.01047.2020 [doi]
AB  - Motor unit (MU) firing rates (FRs) are lower in aged adults, compared with young, 
      at relative voluntary contraction intensities. However, from a variety of 
      independent studies of disparate muscles, the age-related degree of difference in 
      FR among muscles is unclear. Using a standardized statistical approach with data 
      derived from primary studies, we quantified differences in FRs across several 
      muscles between younger and older adults. The data set included 12 different 
      muscles in young (18-35 yr) and older adults (62-93 yr) from 18 published and one 
      unpublished study. Experiments recorded single MU activity from intramuscular 
      electromyography during constant isometric contraction at different (step-like) 
      voluntary intensities. For each muscle, FR ranges and FR variance explained by 
      voluntary contraction intensity were determined using bootstrapping. 
      Dissimilarity of FR variance among muscles was calculated by Euclidean distances. 
      There were threefold differences in the absolute frequency of FR ranges across 
      muscles in the young (soleus 8-16 and superior trapezius 20-49 Hz), but in the 
      old, FR ranges were more similar and lower for nine out of 12 muscles. In 
      contrast, the explained FR variance from voluntary contraction intensity in the 
      older group had 1.6-fold greater dissimilarity among muscles than the young (P < 
      0.001), with FR variance differences being muscle dependent. Therefore, 
      differences between muscle FR ranges were not explained by how FRs scale to 
      changes in voluntary contraction intensity within each muscle. Instead, FRs were 
      muscle dependent but were more dissimilar among muscles in the older group in 
      their responsiveness to voluntary contraction intensity.NEW & NOTEWORTHY The mean 
      frequency of motor unit firing rates were compared systematically among several 
      muscles and between young and older adults from new and published data sets. 
      Firing rates among muscles were lower and more similar during voluntary isometric 
      contraction in older than younger adults. Firing rate responses from voluntary 
      contraction intensity were muscle dependent and more dissimilar among muscles in 
      the older than young adults.
FAU - Kirk, Eric A
AU  - Kirk EA
AD  - School of Kinesiology, Faculty of Health Sciences, The University of Western 
      Ontario, London, Canada.
FAU - Christie, Anita D
AU  - Christie AD
AD  - School of Kinesiology, Faculty of Health Sciences, The University of Western 
      Ontario, London, Canada.
FAU - Knight, Christopher A
AU  - Knight CA
AUID- ORCID: 0000-0002-6348-3906
AD  - Department of Kinesiology and Applied Physiology, College of Health Sciences, 
      University of Delaware, Newark, Delaware.
FAU - Rice, Charles L
AU  - Rice CL
AD  - School of Kinesiology, Faculty of Health Sciences, The University of Western 
      Ontario, London, Canada.
AD  - Department of Anatomy and Cell Biology, Schulich School of Medicine and 
      Dentistry, The University of Western Ontario, London, Canada.
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20210429
PL  - United States
TA  - J Appl Physiol (1985)
JT  - Journal of applied physiology (Bethesda, Md. : 1985)
JID - 8502536
SB  - IM
MH  - Action Potentials
MH  - Aged
MH  - Electromyography
MH  - Humans
MH  - *Isometric Contraction
MH  - Middle Aged
MH  - *Motor Neurons
MH  - Muscle Contraction
MH  - Muscle, Skeletal
MH  - Young Adult
OTO - NOTNLM
OT  - electromyography
OT  - intramuscular
OT  - neuromuscular
OT  - skeletal
OT  - voluntary
EDAT- 2021/04/30 06:00
MHDA- 2021/07/01 06:00
CRDT- 2021/04/29 17:19
PHST- 2021/04/30 06:00 [pubmed]
PHST- 2021/07/01 06:00 [medline]
PHST- 2021/04/29 17:19 [entrez]
AID - 10.1152/japplphysiol.01047.2020 [doi]
PST - ppublish
SO  - J Appl Physiol (1985). 2021 Jun 1;130(6):1903-1914. doi: 
      10.1152/japplphysiol.01047.2020. Epub 2021 Apr 29.